1. Field of the Invention
The present invention relates to the field of compressed air and gas systems, and more particularly to dryness indicators designed to visually indicate the moisture content of compressed gas or air delivered to a point of use.
2. Description of Prior Art
Typical compressed air or gas produced by a compressor apparatus is saturated with 50% to 100% relative humidity. Removal of this moisture vapor requires that an air/gas drying system be used, such as a refrigerated dryer or an adsorbent type of dryer. Such apparatus are generally very effective, the latter being typically capable of drying compressed air or gas to below-zero dew point levels. Notwithstanding such drying measures, there is unfortunately no guarantee that the compressed air or gas will have the desired dryness by the time it arrives through an air/gas feed system to a downstream point of use. Compressed air lines, various fitting and regulation devices, or improper operation of the dryer system all represent sources of residual moisture vapor entrainment in the air/gas feed system. This means that moisture-treated compressed air or gas may be carrying unwanted moisture vapor when it goes into use as an application.
One area where this problem tends to occur is in paint booth operations where compressed air or gas is used as a propellant to atomize and expel paint from a paint gun. Even though extraordinary measures are often implemented to eliminate moisture vapor at the compressed air/gas source, moisture can still be delivered to the paint gun. In some cases, this may be due to the drying system losing effectiveness due to a malfunction or other problem. However, even if the drying system is operating at full operational efficiency, the lengthy hoses connecting the air source to the paint gun can introduce unwanted moisture vapor into the system. In particular, these hoses can be disconnected and re-connected any number of times throughout the course of a painting application. Each time a disconnection occurs, moisture-laden ambient air is allowed to enter the air/gas line, and will feed through the paint gun until such time as it evacuated from the line and replaced by dry air/gas coming from the air/gas source. Any time there is excess moisture vapor in a paint gun, unwanted fouling can occur that results in a bad and unacceptable paint job. In most cases, the unsuspecting painter will assume the air/gas quality is satisfactory, particularly when there is sophisticated drying equipment operating at the air/gas source.
Various dryness indicators have been proposed for use in compressed air, gas and refrigerant applications. These typically involve the use of a moisture-adsorbing silica gel desiccant that is impregnated with a chemical moisture indicator, such as a cobalt salt. This particular chemical indicator is normally a deep blue color when it is dry, but gradually turns a light pink color in proportion to the amount of moisture that is present as the salt hydrates. The color-indicating desiccant is placed in a transparent or translucent container so that it can be viewed during operations. In a dryness indicator, the color-indicating desiccant is placed in contact with a compressed air/gas stream within a transparent or translucent container, so that the desiccant can be viewed during operations.
Prior art dryness indicators tend to have design features that prevent them from being optimally suited for point-of-use operation adjacent a hand-held air/gas-driven tool, such as a paint gun, where moisture monitoring is most needed. In all of the reference materials reviewed, the prior art dryness indicators form part of a filter/dryer that requires a relatively large quantity of desiccant to effectively remove moisture for a reasonable length of time. This quantity of desiccant is more than that which is required to indicate dryness. The filter/dryers in which prior art dryness indicators are incorporated also tend to include additional elements to condense and remove moisture droplets from the air/gas stream, and to trap oil, line debris and other contaminants. As a result of the foregoing design features, most prior art dryness indicators are large or bulky, and not suitable for attachment to a hand-held tool. Other prior art indicating devices are less bulky, but may not be rugged enough to withstand the environmental conditions in which a point-of-use dryness indicator must operate. Such conditions include shock forces when the tool is disconnected and the dryness indicator (still attached to air/gas hose) is dropped onto the floor. While on the floor, the dryness indicator can also be stepped on and thus subjected to crush forces and other abuses.
It is to solving the foregoing problems that the present invention is directed. What is particularly needed is an improved compressed air/gas dryness indicator that is optimized for point-of-use installation between an air/gas hose and an air/gas-driven tool, such as a paint gun. Ideally, the dryness indicator needs to provide a visual indication identifying the exact state of dryness of the compressed air/gas line, yet must be unobtrusive and afford full freedom of movement at the point-of-use without any impediment of bulky filters, desiccant containers, cumbersome vessels, etc. The dryness indicator additionally needs to be rugged and durable, so as to withstand the shock and crush forces that are likely to be experienced during everyday use when the indicator is mounted at the end of an air/gas hose. Finally, the dryness indicator should be easy to install and use, should be simple and inexpensive, and should require no maintenance.